In an optical WDM transmission network, optical signals having a plurality of optical channels at individual wavelengths are transmitted from one location to another. An important element in WDM technology is a reconfigurable optical add/drop multiplexing (ROADM)-based node, which can take in signals at multiple wavelengths and selectively drop some of these wavelengths locally, while letting others pass through. Such capabilities provide the WDM network with flexibility and reconfigurability.
An ideal ROADM-based node has three important features, which are referred to colorless, directionless and contentionless. A colorless node is a node in which each add/drop port of the node is not wavelength selective; any wavelength can be added or dropped at any transponder port. A directionless node is node in which an add/drop channel at the node is not degree selective; any wavelength added on a transponder port can be directed to any outbound nodal degree, and vice versa. A contentionless node is a node in which the same wavelength can be added to or dropped from multiple degrees at the same time to any available transponder port.